[PARISC] Fix palo target

Hunk missing from previous commit, oops.

Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
diff --git a/arch/parisc/Makefile b/arch/parisc/Makefile
index 3f1faca..f93c4cd 100644
--- a/arch/parisc/Makefile
+++ b/arch/parisc/Makefile
@@ -79,7 +79,7 @@
 	fi)
 
 palo: vmlinux
-	@if [ -x $PALO ]; then \
+	@if [ ! -x $(PALO) ]; then \
 		echo 'ERROR: Please install palo first (apt-get install palo)';\
 		echo 'or build it from source and install it somewhere in your $$PATH';\
 		false; \